LO from NLO code generation

Hi,

I do not reproduce your issue.
I have run the following code for LO:

import model loop_sm-no_b_mass
generate u b > t d
output
launch
set fixed_scale 170
set mt 170
set mz 9.170000e+01
set aewm1 1.274210e+02 # aewm1
set gf 1.166370e-05 # gf.
set no_parton_cut
set ebeam 980
set lpp1 1
set lpp2 -1
set pdlabel lhapdf
set lhaid 21200

and got as result:
  === Results Summary for run: run_01 tag: tag_1 ===

     Cross-section : 0.7181 +- 0.0005693 pb
     Nb of events : 10000

for the NLO code I ran:
import model loop_sm-no_b_mass
generate u b > t d [LOonly]
output
launch
order=LO
fixed_order=ON
set fixed_scale 170
set mur_ref_fixed 170
set muf_ref_fixed 170
set mt 170
set mz 9.170000e+01
set aewm1 1.274210e+02 # aewm1
set gf 1.166370e-05 # gf.
set no_parton_cut
set ebeam 980
set lpp1 1
set lpp2 -1
set pdlabel lhapdf
set lhaid 21200
set ptj 0.0

and got:

   --------------------------------------------------------------
      Final results and run summary:
      Process u b > t d [LOonly]
      Run at p-pbar collider (980.0 + 980.0 GeV)
      Total cross section: 7.158e-01 +- 4.4e-03 pb
   --------------------------------------------------------------
      Scale variation (computed from histogram information):
          Dynamical_scale_choice 0 (envelope of 9 values):
              7.173e-01 pb +0.0% -1.2%
   --------------------------------------------------------------

Cheers,

Olivier

Hi Olivier,

thanks for the answer. I have a problem with the codes you sent. If I type launch, it starts as usual, and if then I put set mt 170 (for example) it says

Not valid command: set mt 170

and the same happens for any other set ..., I could always modify the parameters in the param_card and run_card, but it would be also interesting to try it with this direct method.

Anyway, I see that for the NLO you have put

generate u b > t d [LOonly]

why this [LOonly]? Which is the difference with [QCD], because I have a problem there, it seems that using [LOonly] works also fine for me, but using [QCD] doesn't.

Thanks again!

Best,
Laura

Hi,

The way to handle this is to wrote those lines in a file (say cmd_lo.txt and cmd_nlo.txt)
and then run the code like
./bin/mg5_aMC ./cmd_lo.txt
and
./bin/mg5_aMC ./cmd_nlo.txt

Do not try to do
./bin/mg5_aMC < ./cmd_lo.txt
In that case the auto-discovery of the switching between questions will not work and you will have the error that you quote.
You can also write code compatible with that method but this is not recommended since we do not guarantee backward compatibility for that method (I'm considering forbidding it completly in the future actually)

[LOonly] is the same as [QCD] but only generates the LO code since you are not running the full NLO code, this is quicker to generate/compile. But I have also run with replacing [LOonly] by [QCD] and get the same result:

   --------------------------------------------------------------
      Final results and run summary:
      Process u b > t d [QCD]
      Run at p-pbar collider (980.0 + 980.0 GeV)
      Total cross section: 7.158e-01 +- 4.4e-03 pb
   --------------------------------------------------------------
      Scale variation (computed from histogram information):
          Dynamical_scale_choice 0 (envelope of 9 values):
              7.173e-01 pb +0.0% -1.2%
   --------------------------------------------------------------

Cheers,

Olivier

>
> why this [LOonly]? Which is the difference with [QCD], because I have a
> problem there, it seems that using [LOonly] works also fine for me, but
> using [QCD] doesn't.

> On 3 Feb 2021, at 14:45, Laura M <email address hidden> wrote:
>
> Question #695342 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/695342
>
> Status: Answered => Open
>
> Laura M is still having a problem:
> Hi Olivier,
>
> thanks for the answer. I have a problem with the codes you sent. If I
> type launch, it starts as usual, and if then I put set mt 170 (for
> example) it says
>
> Not valid command: set mt 170
>
> and the same happens for any other set ..., I could always modify the
> parameters in the param_card and run_card, but it would be also
> interesting to try it with this direct method.
>
> Anyway, I see that for the NLO you have put
>
> generate u b > t d [LOonly]
>
> why this [LOonly]? Which is the difference with [QCD], because I have a
> problem there, it seems that using [LOonly] works also fine for me, but
> using [QCD] doesn't.
>
> Thanks again!
>
> Best,
> Laura
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi Olivier,

Thank you so much for the answer. I managed to get the same as you with such an external file. Knowing how to do it now, I will try to figure out by myself what was the problem when editing the parameters in the param_card and run_card.

Best,
Laura

Thanks Olivier Mattelaer, that solved my question.

Hi,

I think I kind of know where the other problem lies. I did

import model loop_sm-no_b_mass
generate u b > t d [QCD]
output NLOub

and then modified the parameters in the run_card and param_card. I explicitely need to do it like this to show where the issue arises, and not using the ./mg5_aMC ./cmd_nlo.txt. I wanted to compute first the LO result, to check it with my own, so I tried

./bin/calculate_xsec

set order to LO, and I got sigmaLO_using_calculatexsec = 0.761(6) pb

but if I use

./bin/generate_events

set order to LO also, I get sigmaLO_using_generateevents = 0.718(1) pb

I then looked a bit more carefully the calculate_xsec information given after I changed the order, and there was a line saying:

INFO: will run in mode: NLO

even though I changed it to LO. I tried it in another computer and the same issue arises.

I would like to know if this is also your case, or if it has to do with my Madgraph installation. Thank you very much.

Best,
Laura

Thanks Olivier Mattelaer, that solved my question.